Chemical and Physical Papers. 51 



ferment, called under the newer nomenclature acid-proteinase, 

 because it acts in acid medium upon protein, gelatin and con- 

 nective tissues, is present in the stomach of the human being 

 from the time of birth. It is secreted in the fundic, as well 

 as in the pyloric portions of the stomach. Formerly it was 

 quite generally thought that the parietal (delamorphic, oxyn- 

 tic) cells were the pepsin cells, but since the investigation of 

 Heidenhain and his pupils, Langley, and others, the formation 

 of pepsin has been shifted to the chief cells (adelomorphic, 

 principal of central). Pepsin occurs in the mucous membrane 

 only in the preliminary form of its zymogen, pepsinogen. 

 Pepsin is destroyed by soda. If, however, the mucous mem- 

 brane be extracted with a weak soda solution and the extract 

 be then acidified with HCl, a pepsin-containing fluid of good 

 digestive properties is obtained. (Langley.) Therefore, 

 there must be in the mucosa a substance which is not de- 

 stroyed by soda, and which is transformed into pepsin by 

 treatment with acids. 



From pure gastric juice of the dog, Nencki and Sieber, 

 also Pekelharing, have prepared by dialysis and precipita- 

 tion a very pure pepsin. Pekelharing claims to have prepared 

 the purest acid-proteinase thus far obtained, and classes the 

 enzyme among the proteins. His preparation gives the well- 

 known reactions for protein, and on analysis shows the 

 presence of carbon, nitrogen, hydrogen and sulfur in the pro- 

 portions in which they exist in proteins. It contains no phos- 

 phorus, hence is no nucleo-proteid. Chlorin was found to be 

 a constant constituent. Pekelharing's preparation is the 

 most active preparation of this ferment obtained thus far, 

 0.001 milligram in 6 cc. of a 0.2 per cent. HCl solution dis- 

 solved a flake of fibrin in a few hours. 



Pepsin splits the proteins into a number of difi'erent sub- 

 stances. The farther the cleavage proceeds the simpler will 

 the composition of these substances be. These substances 

 may be separated one from another by fractional precipita- 

 tion with ammonium sulfate. 



The nature of the products formed by this cleavage have 

 been very thoroughly investigated within the past few years. 

 Where we once believed that proteoses and peptones consti- 

 tuted the final products of gastric digestion, ready for ab- 

 sorption and assimilation, we now know that a large number 

 of substances which were formerly looked upon as produced 



